1. Field of the Invention
The present invention relates to an illumination system, and more particularly, relates to a switchable dual-lamp illumination system.
2. Descriptions of the Related Art
In modern household audio/video products, the luminance and service life of the illumination system thereof are two quality determinant factors. For example, since a lamp is commonly used in the projection apparatus as the light source of the illumination system thereof, the luminance and service life of the lamp directly determines the imaging quality and service life of the projection apparatus. However, these two factors are in conflict with each other and difficult to achieve simultaneously. More particularly, a lamp operating with a higher luminance tends to have a shorter service life; on the other hand, if a longer service life is desired, the luminance of the lamp will have to be reduced during the use of the projection apparatus.
In order to overcome such a shortcoming and improve both the luminance and service life of an illumination system simultaneously, a dual-lamp illumination system has been proposed in the prior art in an attempt to improve both the luminance and the service life by using multiple light sources. Moreover, the dual-lamp illumination system also has an improved stability. Specifically, if one of the lamps in the illumination system fails to work during operation, the other working lamp may take its place to maintain continuous operation of the projection system.
There are currently two known kinds of dual-lamp illumination systems that can be used in projection apparatuses: the mechanically switchable dual-lamp illumination system, and the operating type dual-lamp illumination system. The former system only has one illuminated lamp at any given time, and if the working lamp fails, the backup lamp in the dual-lamp illumination system can be manually or electrically moved into the optical path using a mechanical sliding rail. However, temporary loss of the light source will occur in the projection apparatus during the lamp switching process, leading to an interruption in picture display. Furthermore, switching the lamps by means of a sliding rail entails a complicated mechanism which is typically bulky. The bulkiness is undesirable when trying to keep the size of the projection apparatus small.
In contrast, by adjusting the respective reflecting covers in the conventional operating type dual-lamp illumination system, the two lamps are illuminated simultaneously to provide light rays respectively in the optical path. However, a disadvantage of such an illumination system is that it requires a complicated optical path design, and to efficiently utilize the light rays provided by both lamps, the reflecting covers of both lamps have to be cut, molded and adjusted precisely to achieve an expected illumination profile and intensity that should have been provided by a single lamp. Moreover, both of the light rays passing through a multiple complex reflecting light paths may be destructive which leads to a low light utilization efficiency. The equivalent efficiency of either lamp is only about 60% to 70% of an original single lamp. Therefore, it is relatively difficult to obtain an improved stability of the illumination system, i.e., if one of the lamps failed to work, the complete dual-lamp light source must be replaced entirely, rather than using the remaining lamp to maintain continuous operation of the system.
As described above, if either of the lamps fails in a conventional dual-lamp illumination system, it will be difficult to provide a continuous light, thus causing instability in displaying pictures of the projection apparatus. As a result, it is important to provide an improved dual-lamp illumination system which, in addition to having improved luminance and service life, may also allow for stable operation.